The invention resides in a water pump for pumping coolant in a low temperature and in a high temperature circuit including a low temperature housing with an internal low temperature housing, a high temperature housing with an internal high temperature spiral, a water pump impeller for pumping at the same time coolant in the low temperature housing spiral and in the high temperature housing spiral, and a drive shaft for driving the water pump impeller.
DE 41 14 704 C1 discloses a cooling circuit for two-stage charge air cooling. The cooling circuit comprises, a high-temperature and a low-temperature circuit. In the high temperature circuit, in series, a high temperature heat exchanger, a high temperature charge air cooler provided as a first cooling stage, a water pump for circulating coolant in the high-temperature circuit and the internal combustion engine are arranged. In the low temperature circuit, in series, a low-temperature heat exchanger, a low temperature charge air cooler forming a second cooling stage, an engine-oil heat exchanger, a transmission fluid heat exchanger and a second water pump for circulating coolant in the low-temperature circuit are arranged.
In praxis, the first and the second coolant pumps are double suction pumps disposed on a common drive shaft in a two-part housing. In order to keep the weight and the power requirements of the coolant pumps low, the housing and the coolant pump rotors consist of aluminum. In order to further reduce weight, the coolant pump rotor for circulating coolant in the low-temperature circuit is formed integrally with the coolant pump rotor for circulating the coolant in the high-temperature circuit. It is noted however that, with the good heat conductivity of the aluminum and the temperature difference between the high temperature and the low temperature circuit of for example 40° C., an undesirable heat transfer occurs between the two cooling circuits. This heat transfer can be compensated for in the low temperature circuit only by an increased heat removal for example via larger heat exchangers.
It is the object of the present invention to provide a water pump for pumping coolant in a low temperature and a high temperature coolant circuit in which the heat transfer via a common pump rotor is reduced.